REVIEW ARTICLE Shoulder impingement Richard de Villiers MB ChB, MMed (Rad Dj Drs Van Wageningen & Partners PO Box 317 Somerset West 7129 Introduction Shoulder impingement syndrome is probably the most common painful condition of the shoulder. Dynamic compression of the rotator cuff ten- dons in the subacromial space with arm elevation causes intlammation and pain. Three types of shoulder impinge- ment occur: subacromial, posterior and subcoracoid. Subacromial impingement is by far the most com- mon, while the latter two are rare and will not be discussed further. Clinical aspects The patient with subacromial impingement complains of night pain and pain with certain movements, e.g. abduction of the arm. On examin- ation pain is felt through a range of 60° - 120° when the arm is elevated (the painful arc). Neer's sign,' elicited by stabilising the scapula and abduct- ing the arm to above 90°, is positive. Neer's test,' where local anaesthetic is injected into the subacromial bursa, relieves the symptoms. Pathophysiology Neer' described three progressive stages of shoulder impingement: (t) stage 1 - reversible oedema and haemorrhage about the rotator cuff, typically affecting patients below 25 years of age; (it) stage 2 - fibrosis and tendinosis in the rotator cuff, usu- ally seen in patients between the ages of 25 and 40 years; and (iii) stage 3 - tendon rupture and subacromial spurs occurring in the older patient. The basis for the shoulder impingement syndrome is the restricted space that exists between the coracohumeral arch above and the humeral head and tuberosities below. The rotator cuff tendons, biceps ten- don and the coracohumeral ligament pass through this space. The subacro- mial bursa aids in passage of these structures. Compression of these structures is also minimised by a nor- mal acromioclavicular joint, a cora- coacromial arch that allows free pas- sage of the rotator cuff mechanism and normal capsular laxity. Laxity may be increased or decreased, and both may cause secondary impinge- ment due to altered biomechanics of the shoulder during movement. Anterior instability allows the humeral head to translate anteriorly with mechanical impingement of the supraspinatus tendon on the cora- coacromial arch. The supraspinatus tendon is vulnerable to injury because of a relatively avascular critical zone near the site of attachment of the ten- don to the greater tuberosity and anatomical variations in the anterior excursion and slope of the acromion and the shape of its inferior margin.' 26 SA JOURNAL OF RADIOLOGY • February 2003 Rotator cuff calcification Rotator cuff calcification affects about 7% of the population and is a common mechanical cause of sub- acromial impingement. The calcifica- tion may also cause pain, tenderness, swelling and restricted movement. The cause of the calcification is unknown, but may be related to meta- bolic abnormalities and trauma. The calcification is most commonly in the supraspinatus tendon, but may involve the bursa or infraspinatus, teres minor, subscapularis, biceps and pectoralis major tendons. The follow- ing sequence of rotator cuff calcifica- tion may occur: (t) silent (asympto- matic deposition of calcium hy- droxyapatite); (ii) mechanical phase (tendinous calcification causes eleva- tion of the bursa with subacromial bursitis, subbursal or intrabursal rup- ture); or (iit) adhesive periarthritis. There is no significant correlation between the size of the calcification, radiographic appearance and the clin- ical symptoms. Irregular, poorly defined calcification is associated with acute tlares of pain, while well-defined calcification is not." Classification of shoulder impingement Several attempts at classification of impingement have been made. Matsen' classifies causative factors of impingement into two groups, viz. structural and functional factors. Structural factors relate to AC joint (osteophytes and congenital anom- alies), acromion (shape, os acromiale or osteophytes), coracoid process (congenital or post-traumatic), sub- REVIEW ARTICLE acromial bursa (inflammation or thickening), rotator cuff (calcification, thickening or post-traumatic thicken- ing) or humerus (congenital or frac- ture with varus malunion or superior malunion of the greater tuberosity). Functional factors include abnormali- ties in position or motion of the scapula, disruption of the mechanism leading to normal depression of the humeral head, capsular laxity and capsular stiffness. Fu and associates" also divided impingement disorders into two groups, namely primary and secondary impingement. Primary impingement occurs mainly in non- athletic persons and is related to alter- ations in the coracoacromial arch. Secondary impingement occurs mainly in athletes involved in sports requiring overhead movement of the arm and related to either gleno- humeral or scapular instability. X-ray views shoulder impingement A standard impingement series should include the following: (i) AP shoulder with internal rotation; (it) AP shoulder with external rota- tion; (iit) true AP shoulder; (iv) Neer's supraspinatus outlet view (Fig. I); and (v) axial view. AP shoulder with internal rotation This view shows the greater tuberosity in profile and is important to demonstrate a fracture of the greater tuberosity in a patient who has fallen on the tip of the shoulder. AP shoulder with external rotation This view shows the posterolateral Fig. 1. Outlet view. Type 3 or hooked acromion (arrow). aspect of the humeral head in profile and demonstrates the Hill-Sachs deformity of the humeral head after a dislocation. True AP shoulder This view shows the glenohumeral joint space optimally. The blade of the scapula is at 90° to the primary beam. Neer's supraspinatus outlet view This view demonstrates the type of acromion as well as bony causes of supraspinatus impingement, e.g. acromial spur formation. An os aero- miale may also be seen. Axial view This view demonstrates the rela- tionship of the glenoid and the humeral head. Abnormalities of the acromion, coracoid and AC joint are well demonstrated. Additional views 1. Westpoint view: the anteroinfe- rior aspect of the glenoid rim is well assessed for the presence of a bony Bankart lesion or calcification sug- gesting a chronic soft tissue injury. 27 SA JOURNAL OF RADIOLOGY • February 2003 2. Angled AP view of the acromion: AC joint osteophytes, os acromiale and a type 3, hooked acromion can be demonstrated. 3. Bicipital groove view: osteo- phytic spurs or calcification causing biceps tenosynovitis may be seen.' Review of local.. . opinions In shoulder impingement reporting A questionnaire was sent to a group of 35 radiologists and orthopaedic surgeons. They were asked to comment on the style of reporting acceptable in their working environment and relevance of the standard impingement series of the shoulder. Respondents varied in their response to the need for mentioning positive or negative findings in the report. They most often commented on the width of the subacromial space and the presence or absence of acro- mial spurs. The orthopaedic surgeons made special note of the importance of bony spurs. The AC joint, gleno- humeral joint, rotator cuff calcifica- tion and bone texture were all part of the routine radiological assessment. One observer made a very in1por-· tant statement: 'My philosophy in reporting shoulder films is to ensure that even if the X-rays are not avail- able at the time of performing a sub- sequent examination, e.g. shoulder MR! or ultrasound, the report of the X-rays should be detailed enough to give one a good mental picture. Ideally the X-rays should be available before a , scan. REVtEW ARTICLE Recommended report on shoul- der impingement series Prior to dictating a meaningful report, the radiologist assesses the fol- lowing features on the films. The acromion 1. Profile: types 1, 2 and 3. High association between rotator cuff tears and type 3 acromions. 2. Os acromiale. 3. Lateral downsloping of the acromion. 4. Acromial osteophyte formation. Acromioclavicular joint Acromioclavicular joint arthrosis and osteophyte formation may be the primary cause of the patient's pain, or may cause supraspinatus impinge- ment or subacromial bursitis. Greater tuberosity and glenohumeral joint Sclerosis and irregularity of the greater tuberosity is associated with chronic impingement. Assess for frac- tures, Hill-Sachs deformity and loose bodies. Acromiohumeral interval (AHI) AHI less than 1 cm with a break in the 'Shenton line' of the shoulder implies rotator cuff dysfunction (weakness or tear). Rotator cuff calcification Position of the calcification IS important. It may follow acute trau- ma or represent the result of ischaemie tendinosis after chronic impingement (Fig. 2). Fig. 2. Calcification in supraspinatus tendon (arrow) with subbursal rupture. Post -traumatic osteolysis This is a post-traumatic inflam- matory arthritis and is cured by debridement. A suggested normal report is as follows: 'The acromioclavicular and glenohumeral joints are normal. There is no rotator cuff calcification or bony spur formation'. With the appropriate films and a knowledge of the implications of the various radiological findings, positive findings are conveyed by the report and may establish the cause of the painful shoulder. References 1. Neer CS. Anterior acromioplasty for chronic impingement syndrome in the shoulder: A pre- liminary report. J Bone Joint Surg 1972; 54: 41. 2. Resnick D, Kang H. Shoulder. In: Resnick D, Kang H, eds. Internal Derangements of Joints: Emphasis on MR Imaging. Philadelphia: WE Saunders, 1997: 182-214. 3. Rupp S, Seil R. Tendinosis calcarea of the rota- tor cuff. Orthpade 2000; 29: 852-857. 4. Uhthoff HK, Loehr lW. Tendinopathy of the rotator cuff. Pathogenesis, diagnosis and man- agement. JAm Acad Orthop Surg 1997; 5: 183- 191. 5. Matsen FA, Arntz CT. The Shoulder. Philadelphia: WE Saunders, 1990: 623. 6. Fu FH, Harner CD, Klein AH. Shoulder impingement syndrome. A critical review. Clin Orthop 1991; 269: 162. 7. Anderson IF, Read lW, Steinweg J. Atlas of Imaging in Sports Medicine. Sydney: McGraw- Hill, 1998: 96-100. 28 SA JOURNAL OF RADIOLOGY • February 2003